1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light [herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays gamma-rays and the like].
2. Description of the Prior Art
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photoconductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/(I.sub.d)], absorption spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. Particularly, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon [hereinafter referred to as a-Si] has recently attracted attention as a photoconductive material. For example, publications of German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and a publication of German Laid-Open Patent Publication No. 2933411 an application of a-Si for use in a photoelectric converting reading device.
However, under the present situation, the photoconductive members of the prior art having photoconductive layers constituted of a-Si are further required to be improved in a balance of overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics during use such as humidity resistance, and further stability with lapse of time.
For instance, when applied in an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are scheduled to be effected at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigue by repeated uses or so called ghost phenomenon wherein residual images are formed.
Further, according to a large number of experiments by the present inventors, a-Si as the material constituting the photoconductive layer of an image forming member for electrophotography, while it has a number of advantages, as compared with inorganic photoconductive materials such as Se, CdS, ZnO and etc., or organic photoconductive materials such as PVCz TNF and etc., of prior art, is also found to have problems to be solved. Namely, when charging treatment is applied for formation of electrostatic images on the photoconductive layer of an image forming member for electrophotography having a photoconductive member constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of prior art, dark decay is markedly rapid, whereby it is difficult to apply a conventional electrophotographic process. Moreover, this tendency is further pronounced under a humid atmosphere to such an extent in some cases that no charge is retained at all before development treatment.
Further, a-Si materials may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, boron atoms, phosphorus atoms, etc. for controlling the electroconduction type as well as other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical or photoconductive characteristics of the layer formed.
Especially, in the vicinity of the surface or at the interface between the layers adjacent to each other, the problems of behavior of the charges which will be changed variously depending on the kind of the atoms contained, their concentrations and profiles of distribution or stability of the structure become very important controlling this part is often a key for having the photoconductive member exhibit its function as desired to control to have a photoconductive member exhibit its function as desired.
Particularly, when a-Si photosensitive member is prepared by a method generally known in the art, difficulties are encountered in many cases such as repeating characteristics of images or durability thereof. While its mechanism has not been clarified so far, insufficiency with respect to repeating characteristic may be presumably the problem of the capacity of transporting charges in the vicinity of the surface or at the layer interface, and insufficiency with respect to durability may be caused by the structural change in the vicinity of the surface or at that layer interface. Accordingly, the layer design near the interface may be not improved on the basis of factors slightly different from that in the bulk portion.